Red Dead Redemption: this town is unlikely to be big enough for all of us

There are certain games you love from the very first moments. Half-Life was a classic example – its opening sequence was so assured and so immersive, it set you up perfectly for the grandstanding adventure to come. Super Mario 64 with its immediately captivating world was the same… For me, Red Dead Redemption will surely soon be on that list.

I played the finished code for four hours last week and the first time I whistled for my horse and it galloped toward me, muscles rippling, utterly convincing animation (they motion captured a horse – on a treadmill) that was it, I was in. For the first ten minutes, I just trotted up and down the dusty streets of Armadillo, lapping up the perfectly replicated Western iconography; the lone rider slowly sauntering into town, the drunken gunmen lounging on the steps of the saloon, the prostitutes languidly promenading the balconies, the balls of tumbleweed blowing past…

It's 1908 and the outlaw John Marston has been left for dead by his gang after a bloody shoot-out. For him, it's a chance to start again, to settle down with his wife and leave the criminal life way behind him. But as all fans of the Western genre know – no one gets out. Soon, a group of sinister government agents are beating down his door, demanding that he track down his old companions. To secure his services, they kidnap his wife. And the game begins.

Red Dead Redemption is a vast, open-world adventure, featuring the largest landscape Rockstar has ever built, and around 450 individual characters. Alongside the main story missions, players will set off on dozens of minor side-tasks, encounters and objectives, all the time earning fame and – if they behave – honour. In a structural sense, perhaps, it's very much the Grand Theft Auto model, but within a dauntingly immense rural environment that features over 40 different types of animals, an active eco-system, and an astonishingly well-realised sense of history.

Indeed, the early twentieth century setting is a masterstroke. This isn't the mythical heyday of the old west; that culture is in its death throes. Throughout the game, technology is encroaching on the area like a virus. At first, it's the railroads carving through the landscape, but as you travel north you encounter the first confused telephone users bellowing into handsets, and later, the first production line motorcars. John Marston is a man at odds with this coming era; he's a dinosaur. And this sense of growing displacement adds poignancy to the action,

Yet, for the most part, this is a game about wide-open space, about freedom and discovery. One of the worries with a rural setting is that there will be nothing going on out there. But this is not the case. As Rockstar has promised, the landscape is filled with random encounters – you may pass sheriffs chasing down an outlaw, or some poor prospector being bullied by gunmen. Often, I just headed out onto a ridge and watched – in the distance you might pick up the wisps of smoke from gunfire, or dust flying up from a galloping horse; both could lead to profitable encounters. Help a distressed local and they may give you cash, equipment or a treasure map.

The more you do this, the more your honour and fame ratings rise – and soon people will come to you with their troubles. You will, for example, often see a question mark icon on your radar map in the bottom left of the screen; head over and you'll find a civilian with a side-mission – it'll be some sob story about cattle rustlers or a missing family member, but it's another way to make some cash, and some of these will add intriguing long-running sub-plots to your adventure.

But really, the pleasure is just being out there, galloping about, discovering the world. You see armadillos scuttling through the bushes, wolf packs pacing the plains, buffalo slowing trudging along bluffs and breaches. You can hunt animals if you like – shooting and then skinning them to sell their skins at the market. You can also just watch as the sun sets, sending orange rays across the scrublands, or stand out in the billowing rain as the lighting momentarily illuminates some abandoned outpost or hanging tree in the middle of nowhere. There are also numerous GTA-like mini-challenges out here, like shooting a set number of vultures, or blasting a series of items within a time limit. If you're an obsessive completist, you'll be in your element.

Apologies, another quick GTA allusion. In GTA IV, your actions cleverly become part of the social and media landscape; that messy bank robbery you pulled will appear as salacious fodder on the in-game news channel. Here, it's the same. Kind of. You can pick up a newspaper for a dollar and read a report of your last gunfight – it'll be there amid humorous adverts for health-reviving chewing tobacco. Better yet, if you take a ride out into the wilderness at night, you may stumble across groups of travellers telling campfire yarns about your endeavours – a beautiful touch.

The strong sense of characterisation is also hugely familiar: I've seen a fraction of the game, but have already encountered some memorable personalities. Marshal Johnson is a highlight, a laconic and reluctant lawman, just trying to keep his crappy town on the right side of hell. He's given immense gravitas by an excellent voice acting performance that makes a mockery of Heavy Rain's many travails into wooden lifeless recitation. I also loved the dandy New York reporter Jimmy Saint who's come down here to write about the West for the ladies back in NYC. "I'm gonna have some wild adventures!" he cries – and you just know it's going to go horribly wrong for him. And of course, this wouldn't be a Rockstar title without at least one knockabout stereotype – enter Irish, the whisky-swilling ne'er-do-well who'd double cross his grandma for a dram of liquor.

The control mechanic is a successfully refined version of the GTA IV system, with some context-relevant additions. The left trigger draws and aims your gun, an action that's considered provocative by most of the population so it's best not to practice it in a crowded street. The amount of auto-aim is decided by the skill level you select at the beginning of the game. Go for Casual and hitting the button will lock onto a target and stay with them until you let go; in Normal, it'll lock on until you move the right analogue stick, providing some manual ability to re-target; and on Expert, there's no auto-aim at all, cowboy. It's a nice flexible set-up, and though it's easy to pinpoint enemies, these are crude weapons and they don't always fire exactly where you're aiming – a realistic touch that rarely frustrates (perhaps because sometimes my aim was off, but I still managed to clip my target thanks to the vagaries of firing an antiquated Colt pistol at a moving target 50 yards away.)

The right shoulder tab locks you on to cover, from where you can comfortably shoot at enemies without too much exposure. Tapping it again releases you, and it's a really quick mechanic allowing you to build a nice rhythm as you approach an enemy stronghold, snaking in and out of barrels, outhouses and boulders (there's also a crouch mechanic, accessible by pressing the left analogue stick, which adds to your sneaking power.)

The famed Dead Eye system is triggered by pressing the right stick. This slows time and allows you to place pinpoint shots on your target – as long as there's some juice in your gauge (easily charged by buying tonics at the local store, or simply by successfully killing people). Sure, bullet time systems have fallen out of fashion, but this one is awesome fun, bringing to mind Peckinpah's fabulous slow-mo shoot-outs. The system can be upgraded twice throughout the game – at first, you need to manually place your shots, but later the system will automatically pinpoint body areas, so you just have to point, shoot and go and loot the resulting carcass (which is a great way to come by extra cash, ammo and other goodies).

The running mechanic is interesting. You repeatedly hit the A button until you get to the speed you want, then keep it pressed. This works on the horse too, allowing you to reach an impressive gallop – though the beast's stamina wears down quickly, especially when you venture off the dirt tracks and onto rough country terrain. If you're riding with another character, once you've reached the same speed as their horse, you can lock in to a sort of cruise control mode, which allows you to relax and listen to the dialogue – lots of vital mission information is often rattled out en route to the next bloody showdown.

Shoot-outs are just gloriously entertaining. One minute you're pinned in behind a rocky outcrop, taking pot shots with your rifle, the next, you're whistling for your horse, then galloping in, blasting your scuttling enemies as they run for cover. You've probably seen the extravagant bullet impact animations - stricken enemies writhe with each entry, or, when on the wrong end of a shotgun blast, simply fly backwards in a grotesque somersault. It possibly shouldn't be utterly satisfying, but it is. At one point I used Dead Eye to shoot an enemy off his horse, then, as he span hopelessly in the air, plugged him once more before he hit the floor. I'm sorry, but it was beautiful.

Naturally, there's a whole host of weapons to collect, including revolvers, shotguns, sniper rifles, knives and Gatling guns. As you venture toward the north of the map, you'll encounter the first automatic handguns, adding quite a sting to your fire-rate. And of course there's the lasso, for capturing bad guys. Bounty hunting missions are another nice way to earn cash, and you'll usually earn double for bringing the criminals back to the jail in one piece (though mine usually get returned with a few sundry bullet wounds to the legs – well, they run vast, these villains). Brilliantly, there's also a range of equine transport options from mules to thoroughbred stallions; players can even steal a stage coach and scorch through the wilderness with four horses under their command (for real fans, one challenge involves a stage coach race.)

I haven't yet sampled the multiplayer, but it's an intriguing prospect. Alongside standard competitive deathmatch and team deathmatch options, you can go for the Free Roam mode, which will drop up to 16 players into a compete rendition of single-player landscape, complete with officers of the law. From here, you can form a posse, hunt animals or engage in challenges – it's essentially a glorified lobby system; but a lobby system in which you and your friends can attack a bear with a hunting knife.

So yes, I'm four hours in, and I can't wait to return. Rockstar San Diego (aided by Rockstar's other studios – they've developed something of a hive mind approach these days) would seem to have created an incredible open-world experience that just oozes Western authenticity. Of course, Leone will be chucked about as a frame of reference, and he's definitely there in the visual poetry of the game, the vultures circling in the dying sunlight, the riders swooping into town through billowing dust clouds.

But more than that, I see the raw brutality and grit, the sheer nihilism, of Peckinpah and Walter Hill. Red Dead Redemption is an existential drama – it's you alone in a chaotic world. You can add to that chaos (the temptation to just mosey into a saloon and shoot the place up is difficult to resist at times) or you can craft some dignity out of it. But there is always somebody out there waiting, somebody you need to kill.

•Red Dead Redemption is released on PS3 and Xbox 360 on 18 May in the US and 21 May in the UK